View full sizeMichael Lloyd/The OregonianRain is usually the culprit when Portland's sewer system combines with runoff and discharges sewage into the Willamette River.

Portland city officials said a blocked sewer pipe sent 1,400 gallons of raw sewage into the Willamette River this morning.

Linc Mann, spokesman for the city's Bureau of Environmental Services said an electronic monitor alarm detected the overflow from a sewer outfall pipe on the east side of the river south of the Morrison Bridge at 9:26 a.m.

During construction, Mann said, sub-contractors for Stacy and Witbeck, Inc. were working to pump sewage around a diversion structure from one manhole to another, when the accidental discharge occurred.

"The manhole they pumped it into was not the correct manhole,'' Mann said. "There was some confusion about what was supposed to happen. The contractor was very responsive when they discovered what happened."

Mann said the problem was discovered at 10:22 a.m., but not before raw sewage overflowed into the river.

Anyone using the river is cautioned to avoid contact with river water near the Morrison Bridge today and tomorrow because of a higher bacteria levels.